International Journal of Coal Geology最新文献

{"title":"Correlations between metapelitic zones and graptolite reflectance in Ordovician successions from northwestern Argentina depicting a complex postdepositional history","authors":"Nexxys C. Herrera Sánchez ,&nbsp;Margarita Do Campo ,&nbsp;Blanca A. Toro ,&nbsp;Fernando Nieto García","doi":"10.1016/j.coal.2025.104723","DOIUrl":"10.1016/j.coal.2025.104723","url":null,"abstract":"<div><div>Correlations between metapelitic zones and organic proxies of thermal maturity, like coal rank, vitrinite reflectance and color alteration index in conodonts, were developed several decades ago and have been widely applied with satisfactory results. In contrast, comparisons between graptolite reflectance and metapelitic zones defined by Kübler Index values, clay mineral assemblages and chlorite geothermometry are scarce. In this study, samples from Ordovician successions in northwestern Argentina, where graptolite reflectance had been previously measured, were analyzed for clay mineral assemblages using X-ray diffraction, Scanning Electron Microscopy with Backscattered Electrons, and Electron Probe. Additionally, the Kübler Index was determined, and a chlorite geothermometer was applied to compare the response of these proxies for diagenetic-metamorphic temperatures and thermal maturity. The studied material was selected from two sections: Los Colorados, in the western part of the Cordillera Oriental, which mainly comprises the Acoite Formation (Early-Middle Ordovician), and Muñayoc, in the eastern part of the Puna highland, corresponding to the Cochinoca-Escaya Magmatic-Sedimentary Complex (Early-Middle Ordovician). The samples coming from the Los Colorados section reveal a clay mineral assemblage consisting of dioctahedral mica, kaolinite, along with scarce chlorite-bearing mixed-layers and chlorite in few cases, exhibiting Kübler Index values indicative of diagenesis (≥ 0.52 Δ°2θ), and corresponding temperatures between 109 and 282 °C. In contrast, samples from the Muñayoc section present a clay mineral assemblage, comprising mainly dioctahedral mica illite, subordinate kaolinite and smectite, associated with chlorite in few samples; Kübler Index values agree with the epizonal zone (≤ 0.32 Δ°2θ), and temperatures ranging from 177 to 321 °C. Notably, these findings show improved correlation with the temperatures derived from graptolite reflectance when considering updated equations between graptolite and vitrinite reflectance. On the other hand, most of the samples from Muñayoc show non equilibrium clay assemblages, as smectite and kaolinite are not stable in the epizone. This fact, along with the absence of chlorite in several samples, is probably a consequence of the hydrothermal alteration that affected the Ordovician rocks in several localities of the Puna region. As any of these approaches has its own limitation factors and sources of uncertainty, the combination of inorganic and organic proxies provide a more robust methodology to outline low-temperature burial pathways. Moreover, the correlation between Kübler Index and equivalent vitrinite reflectance revealed higher geothermal gradients in Puna than in Cordillera Oriental.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"302 ","pages":"Article 104723"},"PeriodicalIF":5.6,"publicationDate":"2025-02-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143453435","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Petrological, mineralogical, and geochemical compositions of the Eocene coals from Senakin Peninsula, South Kalimantan, Indonesia","authors":"Ferian Anggara ,&nbsp;Donatus Hendra Amijaya ,&nbsp;Tim A. Moore ,&nbsp;Azmii Nanda Fadhillah ,&nbsp;Aulia Agus Patria","doi":"10.1016/j.coal.2025.104722","DOIUrl":"10.1016/j.coal.2025.104722","url":null,"abstract":"<div><div>Samples from the Senakin coal bed (Eocene age, Pasir Sub-basin) were analyzed to study the concentration of critical elements and investigate genetic types and enrichment processes. Of particular interest was to determine if an overlying mafic volcanic unit dated to the same age as the overlying Eocene sediments and tonstein layers withing the coal, affected the geochemical composition of the coal bed. Five partings were identified as being mafic-alkali tonsteins. The lower and upper tonsteins are interpreted to originate both from volcanic ash-fall material intermingled with water-borne detrital sediments. The middle tonstein is thought to have originated primarily as an ash-fall. A consistent feature of all partings, however, is that they are characterized by a graupen texture with additional vermicular and vitroclastic textures. The coal samples from the Senakin coal bed are dominated by vitrinite (64 vol%) with subordinate proportions of liptinite (29 vol%), and inertinite (7 vol%). Optical and SEM-EDX measurements of the coal samples showed that the inorganic material is dominantly pyrite, marcasite, quartz, kaolinite, illite, apatite, calcite, Ti oxides, Ti-V-bearing minerals, and a Mo-bearing mineral. Some coal samples from the Senakin coal bed have total rare earth element and yttrium (REY) concentrations up to 283.53 ppm. Furthermore, coals are enriched in REY and some trace elements (e.g., Zr (Hf), Nb (Ta), Ga, Sr, and V). It is hypothesized that the critical enrichments of the Senakin coal bed may be controlled primarily by three factors: (1) mafic-intermediate volcaniclastic rocks whose provenance are possibly from the Pitap and Haruyan Formations, (2) marine water infiltration from overlying sediments into recently buried peat, and/or (3) the occurrence mafic-alkali tonstein layers.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104722"},"PeriodicalIF":5.6,"publicationDate":"2025-02-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422165","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic matter content and its role in shale porosity development with maturity: Insights from Baltic Basin Silurian shales","authors":"Grzegorz P. Lis ,&nbsp;Tomasz Topór ,&nbsp;Maria Mastalerz","doi":"10.1016/j.coal.2025.104713","DOIUrl":"10.1016/j.coal.2025.104713","url":null,"abstract":"<div><div>Porosity, pore size distribution, and surface area are the main petrophysical characteristics indicative of gas storage capacity in shales. This paper investigates the influence of organic matter (OM) content on the evolution of these parameters at different stages of thermal maturity. Ninety-six samples of Silurian shales from the Baltic Basin ranging in maturity from immature to overmature were selected for this study. Porosity evolution was evaluated using N₂ and CO₂ low-pressure gas adsorption. At the immature stage, the samples with high OM content are characterized by lower porosity than the organic-matter-lean samples. At this stage, high OM content leads to the disruption of stiffer mineral framework; mixed organic-mineral framework is more prone to mechanical compaction than mineral framework. At the oil window stage, porosity of OM-rich samples declines due to pore-throat plugging and pore filling by bitumen. At the wet and dry gas generation stage, porosity of OM-rich samples increases mainly due to pore-throats unplugging. Absent or weak correlation between porosity and OM content at the wet and dry gas stages indicates poor development of OM-hosted secondary porosity. High contents of clay minerals in the studied samples fail to provide the rigid mineral framework and pressure shadows necessary for OM-hosted secondary porosity development.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104713"},"PeriodicalIF":5.6,"publicationDate":"2025-02-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143387891","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics of in-situ stress field of coalbed methane reservoir in the eastern margin of Ordos basin","authors":"Kaichao Zhang ,&nbsp;Song Li ,&nbsp;Guanghao Zhong ,&nbsp;Peng Feng ,&nbsp;Chuang Chang ,&nbsp;Hao Li","doi":"10.1016/j.coal.2025.104715","DOIUrl":"10.1016/j.coal.2025.104715","url":null,"abstract":"<div><div>The eastern margin of the Ordos Basin in China holds substantial coalbed methane resources. Nevertheless, coalbed methane production in this region is significantly constrained due to the unclear characteristics of the in-situ stress field within the coal reservoirs. Drawing on extensive coal seam test data, including well testing and hydraulic fracturing, and uses hydraulic fracturing calculation methods, this study conducts a comparative analysis of the in-situ stress characteristics across various CBM blocks in the region. Results indicate that the in-situ stress of the coal reservoirs along the eastern margin of the Ordos Basin predominantly exhibits medium-high stress, with stress levels higher in the south and lower in the north. The stress field is dominated by the inverse fault stress field (<span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>) in the north while in the south, it is characterized by a normal fault stress field (<span><math><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>). The in-situ stress characteristics of the coal seams are primarily governed by burial depth and local structural factors, with the three principal stresses showing a strong linear positive correlation with burial depth. The vertical stress field distinctly exhibits a “three-zoned” distribution. At a depth of 750 m, the in-situ stress relationship is <span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, indicating that the coal reservoir is predominantly under compressive stress. At depths between 750 and 1500 m, the coal seam stress state follows the relationship <span><math><msub><mi>σ</mi><mi>H</mi></msub><mo>≈</mo><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, transitioning into a stress regime characteristic of a transition zone. At a depth of 1500 m, the in-situ stress relationship is <span><math><msub><mi>σ</mi><mi>V</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>H</mi></msub><mo>&gt;</mo><msub><mi>σ</mi><mi>h</mi></msub></math></span>, and the coal reservoir is predominantly characterized by tensile stress. Despite the relatively deep burial depth of the coal seams in the Hancheng block, its location within the Tongchuan-Hancheng fault zone, where north-south faulting is significantly developed, causes substantial local structural effects. As a result, the coal seam stress field in this area remains dominated by reverse faulting.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104715"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143422164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Chemistry imaging and distribution analysis of rare earth elements in coal using LIBS and LA-ICP-MS instruments","authors":"Chet R. Bhatt ,&nbsp;Jinesh C. Jain ,&nbsp;Alexander A. Bol'shakov ,&nbsp;Dustin L. McIntyre","doi":"10.1016/j.coal.2025.104710","DOIUrl":"10.1016/j.coal.2025.104710","url":null,"abstract":"<div><div>Currently, demand for rare earth elements (REEs) increased significantly. Coal is actively evaluated as potential economic sources for extraction of REEs. In this work, laser-induced breakdown spectroscopy (LIBS) was evaluated for rapid estimation of REEs content and their distribution in the natural coal samples. The results were compared with similar laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) measurements. Thirteen coal samples (nine standard samples and five natural samples) were used in this study. Powder samples were pressed into pellets while coal chunks were directly ablated for data recording. Pellets of the powder standard samples were used to optimize the data acquisition system and then data recorded with this optimized system was used to identify the proper data acquisition and analysis models. After establishing the proper data acquisition system and analysis model using the standard samples, natural coal samples in powder form and their chunks were utilized to record LIBS and LA-ICP-MS spectra. Multivariate calibration models were developed using four of the natural samples, which were evaluated by predicting the REE content in the fifth sample. Principal component analysis was performed on the LIBS data obtained from the natural samples and it classified all the samples with high accuracy. Two-dimensional (2D) elemental mapping on coal chunk samples was also performed using both LIBS and LA-ICP-MS to study the distribution of REEs in the samples. The resulting elemental images and their correlations can be used to infer mineral distributions.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104710"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143427996","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nanomechanical properties of anthracite and graphite: The role of heteroatom functional groups and structural evolution","authors":"Yuhui Wang ,&nbsp;Suping Yao ,&nbsp;Hanlin Zheng ,&nbsp;Zhaoxi Zuo ,&nbsp;Yang Liu","doi":"10.1016/j.coal.2025.104714","DOIUrl":"10.1016/j.coal.2025.104714","url":null,"abstract":"<div><div>This study investigates the anthracite and graphite samples from the Hanpoao mining area in Hunan Province, China, to understand their structural deformation characteristics in relation to tectonic stress and magmatic intrusion. Despite previous research highlighting the influence of tectonic stress on the microcrystalline structure of organic matter, there remains a gap in comprehensively understanding how these factors interact and affect the mechanical properties of coal and graphite. To address this, the research employed a combination of optical microscopy, reflectance measurements, Raman spectroscopy, and high-resolution atomic force microscopy, along with powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. Studies have shown that the Young's modulus of anthracite and graphite exhibits a certain correlation with both coal rank and the degree of graphitization. Notably, the presence of heteroatom functional groups, particularly sulfur-containing groups, plays a crucial role in modulating the Young's modulus. The study reveals an inverse correlation between thiophene sulfur content and Young's modulus, and a positive correlation with sulfone and sulfoxide sulfur content, suggesting that these groups significantly influence the mechanical properties of anthracite and graphite. We have done comprehensive investigation of the interplay between coal rank, microcrystalline structure, and heteroatom functional groups on the nanomechanical properties of anthracite and graphite. These studies provide a novel perspective for the assessment of the mechanical properties of coal and coal-based graphite, while also offering important theoretical foundations for the efficient utilization and advanced processing technologies of coal resources.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"301 ","pages":"Article 104714"},"PeriodicalIF":5.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143377574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Intelligent identification of coal macerals using improved semi-supervised semantic segmentation methods","authors":"Na Xu ,&nbsp;Qingfeng Wang ,&nbsp;Pengfei Li ,&nbsp;Jiapei Kong ,&nbsp;Qing Li ,&nbsp;Mark A. Engle ,&nbsp;James C. Hower ,&nbsp;Wei Zhu","doi":"10.1016/j.coal.2025.104712","DOIUrl":"10.1016/j.coal.2025.104712","url":null,"abstract":"<div><div>Recently, the demand for automatic coal maceral identification has gradually received much attention, and hence deep learning has been applied to the identification of coal macerals. However, a large number of labels are necessary for supervised learning, which imposes challenges for automatic coal maceral identification. In this study, the methods for identifying coal macerals were fully reviewed. Considering the limited data and the complexity of annotation, a semi-supervised semantic segmentation model combined with conditional random fields (CRF) algorithm was suggested for pixel-level identification of coal macerals. Initially, a new dataset of coal macerals was established. The dataset contains many different coal maceral images collected from the USA and China, as well as the corresponding labeled images. Then the model was trained through adversarial loss, and the prediction results were evaluated through pixel accuracy (PA) and intersection over union (IoU). The results are compared with other three existing unsupervised image segmentation methods. The semi-supervised model achieved, on average, PA and IoU of 84 % and 74 %, respectively. The results show that semi-supervised semantic segmentation can achieve high-precision identification of coal macerals. The CRF algorithm is then employed on the predictions of the model, and the accuracies for the three coal maceral groups achieved 81 %, 84 %, and 88 %, respectively. Finally, the application results of the model on the testing dataset are discussed to compare the differences between artificial intelligence and manual identification. This study demonstrates that semi-supervised semantic segmentation combined with CRF algorithm can be successfully applied to automatic coal maceral identification.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104712"},"PeriodicalIF":5.6,"publicationDate":"2025-02-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143238665","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanisms of strain rate-dependent response of naturally fractured coal","authors":"Linan Su,&nbsp;Hamid Roshan","doi":"10.1016/j.coal.2025.104711","DOIUrl":"10.1016/j.coal.2025.104711","url":null,"abstract":"<div><div>The mechanical characteristics of naturally fractured coal under strain rate-dependent loadings can affect engineering activities such as coal seam gas production, gas drainage and CO₂ sequestration. While the macro-(core) scale strain-rate dependent response of fractured coal has been investigated previously, the micro-scale mechanisms driving this core-scale behaviour particularly under recoverable (elastic) bulk deformation remains unexplored. In this study, we conduct a series of systematic multi-scale experiments to shed light on the mechanisms controlling the strain rate dependency of coal.</div><div>Core-scale triaxial tests are initially performed on coal specimens under isotropic and deviatoric loading conditions at different strain rates to identify their strain rate dependency. The results indicate a clear strain rate dependency in dry specimens only under isotropic loading, where the bulk modulus increases with increasing strain rates. Notably, unloading of the specimens shows a considerable strain rate-dependent energy dissipation without any permanent deformation in these isotropic loading tests.</div><div>To explore the identified micro-scale processes causing the energy dissipation and strain rate-dependency, a series of micro-scale mechanical tests are conducted on a coal joint specimen, coupled with microscopy and digital image correlation (DIC) analysis. The results from triaxial and micro-scale tests indicate that the asperity damage within pre-existing fractures during their closure is the primary driver of strain rate dependency at core-scale, without inducing any permanent deformation in bulk specimens.</div><div>To gain further insights into the relationship between asperity damage and energy dissipation under varying strain rates, a series of normal stress loading tests are conducted on identical synthetic joint specimens. These tests confirm a strong correlation between asperity damage and energy dissipation in the identical specimens, demonstrating that slower strain rates lead to greater asperity damage, higher energy dissipation, and reduced stiffness. These findings substantially enhance our understanding of asperity damage-driven strain rate dependency of fractured rock through the evolution of energy dissipation.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104711"},"PeriodicalIF":5.6,"publicationDate":"2025-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143237897","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The effect of high pressure on hydrocarbon generation from Type-I kerogen source rocks: Implications for petroleum system evolution","authors":"Ahmed Khairy ,&nbsp;Clement N. Uguna ,&nbsp;Christopher H. Vane ,&nbsp;Waleed Sh. El Diasty ,&nbsp;Kenneth E. Peters ,&nbsp;Colin E. Snape ,&nbsp;Sherif Farouk ,&nbsp;Will Meredith","doi":"10.1016/j.coal.2025.104708","DOIUrl":"10.1016/j.coal.2025.104708","url":null,"abstract":"<div><div>This study examines the effect of high water pressure (up to 900 bar) on hydrocarbon generation from Type-I kerogen-rich source rocks and compares the results with previously observed effects on Type-II and Type-III kerogens. An immature Type-I oil shale sample from the Duwi Formation, Egypt, was pyrolysed under anhydrous, low-pressure hydrous, and high water-pressure conditions at 320 °C (end of bitumen generation) and 350 °C (oil window) for 6 and 24 h, respectively.</div><div>Pyrolysis at 320 °C showed that bitumen generation was promoted in the presence of water under low-pressure hydrous compared to anhydrous conditions but retarded at high water pressures. At 350 °C, oil generation was also retarded by increasing pressure, with maximum oil yield at 500 bar before dropping by 72% at 900 bar. Lower bitumen yields at 500 bar and higher yields at 900 bar confirm more retention of oil and bitumen in the rock at higher pressure. High water pressure systematically decreased hydrocarbon gas yields, with a more prominent effect at 320 °C because of temperature's dominant impact over pressure at 350 °C. Similarly, non-hydrocarbon gas yields decreased as water pressure increased, with maximum yields under anhydrous and low-pressure hydrous conditions. The retardation effect on bitumen generation was less significant than that on oil and gas generation.</div><div>This study highlights pressure's impact on petroleum generation, particularly in overpressured basins. Elevated pressures on Type-I kerogen source rocks retard oil expulsion, and the retained oil and bitumen within the rock can be directly cracked to gas, suggesting that under such conditions, oil yields may be lower, while unconventional gas resources are likely to be more abundant.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104708"},"PeriodicalIF":5.6,"publicationDate":"2025-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143237898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Element geochemical characteristics for the roof and floor rocks of coal seams in the Shendong mining area: Emphasis on hazardous element fluorine","authors":"Zheng Zhang ,&nbsp;Guoqing Li ,&nbsp;Lei Wang","doi":"10.1016/j.coal.2025.104709","DOIUrl":"10.1016/j.coal.2025.104709","url":null,"abstract":"<div><div>The Shendong mining area produces over 200 million tonnes of coal annually, resulting in notable gangue output, including materials from coal roof, floor and gangue itself. The hazardous elements, particularly fluorine (F), present in the gangues pose challenges for energy utilization and safe use of mine water. Despite this, studies on the elemental geochemical characteristics of gangues in the Shendong mining area are limited. This study collected 19 samples of coal roof and floor and employed methods such as SEM-EDS, XRD, XRF and ICP-MS to analyse the mineral compositions and quantify major-element oxides, rare earth elements and yttrium (REY), and most trace elements. Additionally, fluorine concentration was determined using the alkali fusion–ion selective electrode method. Results indicate that fluorine has the highest average concentration (655 μg/g) among the trace elements, with an enrichment coefficient of 1.21. The major minerals identified in the samples include clay minerals, quartz, and feldspar. The REY distribution patterns in the investigated samples predominantly show L-type enrichment. Combined analysis of B/Ga, Sr/Ba, V/Cr, U/Th, Ni/Co and <em>δ</em>U suggest that the coal roof and floor formations occurred in a continental freshwater and oxic sedimentary environment. The material source analysis indicates that coal roof and floor rocks are primarily derived from felsic rocks in the upper continental crust, especially a mixed provenance of granite and calcareous mudstone. Principal component analysis (PCA) reveals that the fluorine primarily exists on the surface of illites in an adsorption state, with Cu, Cs, Se, Th and Rb exhibiting similar states of occurrence. Correlation analyses between fluorine concentrations in the coal roof and floor rocks and parameters of ∑LREY, La_N/Lu_N, and <em>δ</em>Ce suggest that fluorine tends to be enriched in weathering residues; additionally, a weakly oxidising environment appears to facilitate fluorine enrichment in these coal roof and floor rocks. The findings in this study can guide the development of effective strategies to reduce fluorine contamination in the mine water; additionally, they aid in developing approaches to address fluorine-related issues during combustion, thereby promoting the safe and efficient utilization of coal gangue as a supplemental fuel resource.</div></div>","PeriodicalId":13864,"journal":{"name":"International Journal of Coal Geology","volume":"300 ","pages":"Article 104709"},"PeriodicalIF":5.6,"publicationDate":"2025-01-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143083307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}